Coupling cavities of a magnetron without use of straps



March 25, 1958 E. C. OKRESS COUPLING CAVITIES OF A MAGNETRON WITHOUT USEOF STRAPS FileQ. Aug. 20. 1954 Fig. 3

. INVENTOR Ernest C. Okr ess BY ATTORNEY United States Patent COUPLINGCAVITIES OF A MAGNETRON WITHOUT USE OF Ernest -C. Okresg, Elmira, N.,Y., assignor to Westinghouse Electric Corporation, East .Pittshurgh,122., .a ..c0rp.oration oiPennsy-lvania Application August'20, 1954,Serial No. 451,224

11 Claims. (Cl. 315-.39;77)

A- magnetron comprising a meresymmetric system of.

identical cavity resonators arranged-incirou'lar larray about acylindrical cathode can have nodes of electrical oscillation, where N is"the :number of cavities. Of these modes, that one in which alternateresonator segments are of opposite polarity, known as the 71' -mode,- isordinarily desired 'for operation, and it has been wide practice in-theart to provide {straps which interconnectalternate segments with eachother to :provide adequate mode separation and give the 1r mode superiorstability over other possible oscillation modes. However, thestabilization of the 1r mode thus attained proves insuificient withcertain types of loading-and to increase stabilization, discontinuities(breaks) atpoints in the strapping at such angles to the cavity to which'the power offtake (transducer) is attachedas-wiill increase thecoupling to the transducer of competingosc'illation modes has beenresorted to.

Several serious disadvantages have, however, been found to result fromuse of straps, the most serious being a tendency toelectrical breakdownbetween the straps and the resonator segments which they by-pass atseparation-distances which are limited in magnitude by'desig'n factors.High electric gradient, bombardment by electrons emitted by the cathodeand sublimation of electronernissive material deposits on the straps andanode from the cathode surface all contribute to such breakdowntendencies.

In accordance with my present invention lteliminate strapping entirelyand interconnect cavities o'fflike phase by what are essentiallywaveguides at the periphery .of the cylindrical anode structure.

One object of my invention is accordingly to provide an improved methodof stabilizing the 1r mode of oscillation in magnetrons.

Another object is to provide a novel type of magnetron in which the 1rmode of oscillation is highly stabilized.

.Another object is to. provide a novel type of magnetron stabilized forthe 1r mode of oscillation which is capable of operating with highervoltage gradients than stabilized magnetrons of the prior art.

Another object is to provide a magnetron of novel structure in whichthere is a wide frequency separation between the 1r mode .of oscillationand competing modes.

Another object is to provide a novel method of destroying the symmetryof doublet fields of modes competing with the 1r mode of oscillationin amagnetron.-

of the p ages. 19 or z w.;.-- ene a k pea as 2,328,445 Patented. Mar.25,1958

Still another ohjectlistoprovide a novel method of altering thecharacteristic admittance of the resonant system in a cavity-typemagnetron.

.Qther. objects tot-my invention will become evident .uponreadingfhe'following description and referring; .to .theilrawings .in which: s

Fig, 1 is a view partlylin .section of a twelve cavity magnetron.emhodyingtheprinciples .of,my invention;

Fig. ,2Qis .a..section;-.along thev lines 11-11 of Fig.1; and

.Fig, 3 ,adetail section showing :a modified diorin of .my jnvent'iona'nd. .taken along. a. similar .plane to .that of Fig. l.

.Re'ferring inL-detailto Fig. 1, .a magnetron. embodying myfiinvenfion.may comprise a:..conventional cylindrical cathode. 1,, flie per ipheral.ativesurface .of which. is indicated by a dotted circle, coaxial with.an ,annularvanode .2 twelve equally spaced cylindrical.cavitvresonators ',3 ,to :14 of similar dimensions. Each resonator .isconnected in usual fashion with the annular inter-action space .15surrounding cathode .1 .by; cavity interaction slot 16Ihavingwallscompr'is'ing parallel planes equally spaced .florn. that.axial plane .of the cathode whichineludes ,flie .Of.'IhB" cylindricalcavity. Near. the

periphery .ofetheanod'e are, at each endeface, annularrectangulangrooves 17 and :18-wh'ich-iare the principal ,-I havepreviously referred to as constitutinguny present invention.

Each odd .(or .even) numbered, cavity resonator .isv connected .tothegroove 17 by .a passage 19 which imavhave arectangiilar section; andeach. even, .(or odd) numbered cavityeresonator is connected tothe-groove 1'8. byia similar passage.21..

The peripheryuofthe cylindrical anode 2..is enclosed by .a wall ofconventional. type whichfhasitsfends, closed in, conventional fashionbyend-walls (not shown). The cavity 3 has .an outlet passage through.wall..22 to which is connectedin well-known fashionawaveguidel l whichmaybe of coaxial .type and which forms agtransducer for power outflowfrom the magnetron. Coupling-of the transducer may beeffected.in,a..well:known;..way 'by a core-rod 25 extendingthroughpassage .23 and forming a .lo-op26. having itsend connected tothe wall of icavityS Flt will be .seen in Figures1 .and. .2 that oddnumbered cavity-resonators are .all,connected'-together by .a wave-.guide comprisingthe-groove-17 and .the.passages...'19, whileallevennumbered cavity-resonators are connected together by a. waveguidecomprising the groove 18v and passages 21. This can .be shown-to resultin altering the inductive couplingwhich exists .between adjacentcavity-resonators .andthis changes the .resonant frequency .of the.system..

.It is possible to increase the insn ranceagainstrany .particularcompeting mode of. oscillation. interferingjwith the 1r mode byintroducing a discontinuity 27 finihe wavetr-ansmission .propertiespfthe. grooves-.17 or 18.by'decreasi-ngor increasing. its cross-sectionata suitable distanceKalong it from thecouplingloop 26;.tov destructivelyinterfere with. sustenance, of. .theconapetmg v.mode .in question. Themutualcoupl-ing between cavities ofiike phase is dependent on the axial1depth fiend wid-thm ofsthe r s v .7 and 18., and the rad all t t i l -tW dth: :23? 1 of the order of the diameter oi-. the;cavities, and: .wandt m be of the order of the w-idth of the;.interaction slots-lii.

0n the other :handt et ial leng h L p ss seszls l non-resonant lowimpedance links, and no large electric gradients can develop in them.

It will be noted that the passages 19 or 21 are remote from the cathode1 where deposits of material sublimed from the cathode and bombardmentby electrons from the interaction space are negligible. The electricfield in the resonator is likewise a minimum there. Hence littletendency to electric arc-over, such as that mentioned above as found instrapped magnetrons, exists in my arrangement. The structure likewiseavoids the use of an asymmetrical resonator system such as those ofrising sun type magnetrons and so eliminates the complexities ofpossible model operation which the duplex cavity-systems of the latterinvolve.

It may be pointed out that the existence of the transducer at one cavityresonator distorts the 11' mode pattern,

of all magnetrons, but that this distortion will be reduced by mypresent arrangement of waveguides interconnecting the cavities of likephase. There is also some 'n' mode pattern distortion due tonon-uniformity of the resonator slot field along the magnetron axis dueto strapping at the ends of the cavities. This distortion is lessenedwhere by present waveguide interconnection system is substituted forprior art strapping.

It is also possible to modify the structure shown in Fig. 1 bysubstituting ridged waveguides for the simple rectangular channels 17and 18 to interconnect cavities of like phase. For a given load thissystem gives an increased stabilization if the ridged waveguide isproportioned to give the desired degree of coupling. Fig. 3 illustratesa ridged waveguide 30 substituted for the channel 17 in Fig. 1. Theridged waveguide is provided with a ridge member 32.

It may be pointed out that the arrangement here disclosed is very muchsimpler to make and operate than are the coaxial loop strapping systemsof the prior art, and is also free of the spurious resonances likely todevelop in strap systems because of their higher impedance and liabilityto resonance in their coupling.

It will also be noted that the coupling passages 19 or 21 need not bepositioned exactly in line with the resonator slots 16, but may beofi-set on one side or the other of that position to attain morecomplete screening from cathode electrons and sublimation deposits fromthe cathode.

I claim as my invention:

1. A magnetron comprising a cylindrical cathode and an anode comprisingan annulus having an even number of cylindrical cavities with axessubstantially parallel to the central axis of said annulus and arrangedwith their axes at points equally spaced on the circumference of acircle concentric with said annulus, a radial interaction slotconnecting each said cavity with the inner surface of said annulus, anannular groove in each end face of each said annulus near the peripherythereof, a first passage from each odd numbered cavity only, said pointpassages connecting said each odd numbered cavity with one said grooveand a second passage for each even numbered cavity only, said secondpassages connecting said each even numbered cavity with the other saidgroove.

2. A magnetron comprising a cylindrical cathode and an anode comprisingan annulus having an even number of cylindrical cavities with axessubstantially parallel to the central axis of said annulus and arrangedwith their axes at points equally spaced on the circumference of acircle concentric with said annulus, and a radial interaction slotconnecting each said cavity with the inner surface and arranged withtheir axes at points equally spaced on the circumference of a circleconcentric with-said annulus,

a radial interaction slot connecting each said cavity with the innerface of said annulus, an annular groove in an end face of said annulusnear the periphery thereof, and a passage for every other cavity only,said passages connecting said every other cavity with said groove.

4. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, an annular groove in each end face of said annulus nearthe periphery thereof, a first passage for each odd numbered cavityonly, said first passages connecting said each odd numbered cavity withone said groove, and a second passage for each odd numbered cavity only,said second passages connecting said each even numbered cavity with theother said groove.

5. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on of said annulus, an annular groove in an end face of saidannulus near the periphery thereof, a passage for every other cavityonly, said passage connecting said every other cavity with said annulargroove.

3. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus the circumference of a circle concentric with saidannulus, a radial interaction slot connecting each said cavity with theinner face of said annulus, an annular groove in one end face of saidannulus near the periphery thereof, a passage connecting every othercavity with said groove, and a section of altered cross-section at onepoint in said groove.

6. A11 anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, an annular groove in each end face of said annulus nearthe periphery thereof, a passage connecting each odd numbered cavitywith one said groove, a passage connecting each even numbered cavitywith the other said groove, and a section of altered cross-section ineach said groove.

7. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, a ridged waveguide encircling the periphery of saidannulus at one end face thereof and a passage connecting every othercavity with said ridged waveguide.

8. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, a ridged waveguide encircling the periphery of saidannulus at each end face thereof, a passage connecting each odd numberedcavity m'th one said waveguide, and a passage connecting each evennumbered cavity with the other said waveguide.

9. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, a ridged waveguide encircling the periphery of saidannulus at one end face thereof, a passage connecting every other cavitywith said ridged waveguide, and a section of altered cross-section atone point in said waveguide.

10. An anode for a magnetron comprising an annulus having an even numberof cylindrical cavities with axes substantially parallel to the centralaxis of said annulus and arranged with their axes at points equallyspaced on the circumference of a circle concentric with said annulus, aradial interaction slot connecting each said cavity with the inner faceof said annulus, a ridged waveguide encircling the periphery of saidannulus at each end face thereof, a passage connecting each odd numberedcavity with one said waveguide, a passage connecting each even numberedcavity with the other said waveguide, and a section of alteredcross-section at one point in each said waveguide.

11. A magnetron comprising a central cathode surrounded by an anode,said anode comprising a plurality of segments projecting inwardly towardsaid cathode, said segments separated by cavity resonators, an annulargroove in an end face of said anode near the periphery thereof and apassage for every other cavity resonator only, said passages connectingsaid every other cavity resonator with said groove.

References Cited in the file of this patent UNITED STATES PATENTS2,408,234 Spencer Sept. 24, 1946 2,611,110 Powers Sept. 16, 1952

